TWO WATER TESTING METHODS
COULD PROVE USEFUL IN PREDICTING EFFECTS OF GLOBAL CLIMATE CHANGE

COLUMBUS, Ohio – Ohio State University geologists and their colleagues
have used two water-testing methods together for the first time to help
a Gulf Coast tourist community manage its water supply.

The two methods could prove useful for gauging how rising sea levels
-- one of the possible effects of global climate change -- might cause
salt water to infiltrate drinking water along coastal areas in the future.

Anne
Carey

Anne
Carey, assistant professor of geological
sciences at Ohio State, likened Baldwin County in southwestern Alabama
-- where the study was conducted -- to the Chesapeake Bay area, where
rising seawater has already covered some islands and ruined agriculture
on others.

“Sea level is rising in places where coastal development is rapid,”
Carey said. “Some wells have been abandoned in Baldwin County due
to salt water intrusion. Increased water usage and sea-level rise are
likely to exacerbate the problem.”

To map water usage, geologists often measure the age of water taken
from different sites around a region. The age suggests how quickly rainwater
renews the water supply, and how quickly seawater could potentially enter
the system.

Any prediction of how quickly global
climate change could cause salt water to infiltrate Baldwin County
would require further study, Carey said. But this early work shows
that scientists can use both dating methods simultaneously to
get a more reliable view of water usage.

The Alabama site was ideal for Carolyn Dowling, a post-doctoral investigator
with Ohio State’s
Byrd Polar Research Center, to compare two different methods of water
dating for her doctoral dissertation. One was the well-known radiocarbon
dating, which measures the presence of the isotope carbon-14, while the
other was a lesser-known method that measured the isotope helium-4.

Though scientists long thought the two methods were incompatible, Carey
and Dowling successfully used both together to determine that ages in
different wells ranged from 50 years to 7,500 years. The results appear
in a recent issue of the Geological
Society of America journal Geology.

Carbon dating placed the ages of water from different wells in a range
of approximately 375 to 7,000 years old, and the helium method suggested
a similar range -- 50 to 7,500 years old.

To Carey, the ages themselves are not particularly surprising.

“This isn't really, really old water -- it's all from the Holocene,
the period since the last ice age,” she said. “In northern
Ohio, there are places where people are pumping Pleistocene
water [more than 10,000 years old].”

“It was startling to the well operators that their waters were
that old, but it isn’t a startling story geologically,” she
continued. “The important part of the research is that we could
show the nice correspondence between the two methods, which has never
been done before.”

Any prediction of how quickly global climate change could cause salt
water to infiltrate Baldwin County would require further study, Carey
said. But this early work shows that scientists can use both dating methods
simultaneously to get a more reliable view of water usage.

“Any time you can measure something with two different methods,
you can be more confident in the results,” she said.

Water usage in Baldwin County surges during the spring and summer tourist
seasons, when turf grass farms also draw on freshwater supplies for irrigation.
More than 20 percent of the county is water, and its extensive lowlands
would make it particularly susceptible to flooding, should water levels
rise in the Gulf of Mexico.

Carey, Dowling, and colleague Robert Poreda at the University
of Rochester tested the water from 12 wells around Baldwin County
using both methods.

Carbon dating measures how much carbon-14 is left in the water since
the last time the water contacted carbon dioxide in the air. Helium dating
measures how much helium has dissolved into the water from surrounding
rock as it lay underground. Both give scientists a measure of how long
water has been in a particular well or aquifer.

The results also suggested that the Baldwin County well operators are
doing a good job of drawing fresh water from the right places at the right
time to keep salt water from entering the system for now.

Saltwater infiltration could become a bigger issue in the future with
global climate change.

Over the last 100 years, sea level worldwide has risen an average of 2
millimeters per year. The melting of tropical glaciers and polar ice caps,
which scientists have documented in recent years, could increase that
rate. A warmer climate would also heat the oceans, causing them to expand
-- and sea level to rise further.